Purification of gases



Patented Sept. 3, 1935 a A.

'U-NlTEDr srAr-rsgsfl Jesse G, Melendy, Tarrytown- N. Y as sign6r m1; i a General Chemical Company New York,N.Y.,a,. 1 3

corporationof. New York 'No' Drawingn- Application July}, 1931,

Serial No. 549.806 1 v s 4 Claims. ('01. "ea-+1173)v This invention relates to a method for the puri-' fication of burner gases such as are produced from sulfur or sulfide ores andother materials employed as a source of sulfur the manufac-" S ature of sulfuric acid. The inventionis directed especially to a purification processwhich will render sulfurous gases suitable'for the manufacture: of sulfuric anhydride and sulfuric acid by the so-called contactprocess in which the sulfur 1O%-*- dioxide.-content in such gases is caused" to corribine withoxygen bycatalytic action, particu larly when platinum is used as the catalyst.

The invention more particularly relates to and constitutes an improvement'of purification and drying processes as are disclosed in U; S. Patcooling towers arranged in series. In the cooling towers, the gases are cooled generally to something less than about 300 F., solid impurities removed from the gases, and the moisture content thereof is materially increased. The

temperature of the partially cooled gases is then further reduced by passage through coolers, such ifor example, as those shown in the later Herreshoif patent. During the passage of the gas through these coolers, the larger portion of the water vapor is condensed, and then withdrawn from the system through suitable outlets in the base of the cooling chambers. At this stage,the gases have been purified toa considerable degree, and most of the moisture has been removed therefrom. The gasesin this condition are then conducted into so-called coke filters which effect removal from the gas stream of the sulfuric acid mist. Further quantities of moisture and arsenic contained in the mist are also removed from the gases by the coke filter. From the filter, the gas stream is passed through drying towers in contact with concentrated sulfuric acid to substantially completely dry the gases before permitting the same to pass through the blowers in the gas line and thence into the conversion chambers.

I The presence of fluorine as an impurity in burner gases hasbeen known, and the deleterious effect of this substance on catalysts; for example platinum, is also familiar. Several methods and modes of treatment have-been proposed looking primarily toward the elimination of fluo- 1 rine from the burner gases before the latter are conducted into contact with the *cataly'stu Iheserprior proposals have. succeeded in. eliminating, fluorine an'd other; impurities from the gas-stream. to a'satisfactory extent in m'anycases; 'Imotherx. cases, however, operationofthe systemhas'lbee'np found to result in gradualdeterioration oflthe- 1' into the. catalystwith. resulting poisoning there; 1

0f.- The primary 1 object of the present invention is -t' to provide amethod-for further and substantially complete removal of fluorine from burner gases containing the l samean'd particularly fr'om "209 burner ga-ses containing relatively large amounts of fluorine which are not removed to a sufiicient extent by the usual purification methods. According to the present invention, it has been found that burner gases containing fluorine im- 25 purities may be dried and simultaneously the fluorine impurities removed therefrom by treating the gases with strong sulfuric acid, and preferably by contacting the gases with sulfuric acid of strength of about 98%. 30

The treatment of the burner gases with strong acid may be carried out as a separate step, but it has been found that the elimination of fluorine impurities and final. drying of gases just prior to the conversion operation may be advan- 35 tageously combined and effected in a single treatment. Accordingly, in thepreferred embodiment of the invention, the gases are dried and substantially all the fluorine impurities removed therefrom by' contacting the gases with strong 40 sulfuric acid in a tower such as, for example, the tower P of the Herreshoff Patent 940,595, located in the gas line just ahead of the gas heater and first converter or the blower, if the system be such that blowers are employed in the gas line 45 between the purification train and the convert-. ers. Briefly stated, the objects and purposes of the invention may be accomplished by contacting the gases with strong sulfuric acid circulated through a final drying tower such as the tower P 50 disclosed in the earlier of the Herreshofi patents above noted.

As noted, the invention contemplates a treatment with strong sulfuric acid as distinguished from -66" Be. sulfuric acid, usually considered 55 lcordance with my invention exerts a strong ab-' sorbing effect for fluorine impurities as compared I to Weaker drying acid but irrespective of the explanation of the phenomena it has been found I that the strong acid satisfactorily purifies burner gas of. fluorine impurities so that the'gas may be subsequently passed, to the catalyst, without pois oning thereof, whereas, acid of less than 95% 1 strength when used on the same gas did not satis .factorily purify the gas of fluorine impurities and gradual poisoning of the catalyst resulted. ;.In- Vestigations indicatethat a hydrofluoric acid cone tentin excess of 0.0000001 gram perfcubic .foot of gasmay cause appreciable poisoning of thecata-- lyst. sHence; the inventionis, particularly ap-i plicable: to the treatment of gases containing in The tower employed for contacting the gases --:and the strong acid maybe of the usual construe-g tion', for example one containingsuitable packing through which the gases are passed upwardly in contact ,with the downwardly flowing acid,.the circulation-of which-through the tower may be gnaintainedby the necessary pumps and piping.

It will be seen that the preferred embodimentv of; the invention, i.' e. where the drying: of the acid and thejremoval of fluorine impurities therefrom, are carried out in a; single step-in a'tower. in the =;-5gaS:1ine just-ahead of-the heaters and converters,=* provides a process by which a substantially com- 7;

It is not plete removal of fluorine from the gases is eifected together with a simultaneous drying of the gases to the necessary degree.

The invention is, of course, not limited for use in conjunction with a purification system such as; 5

' disclosed in the Herreshoifpatents. The present invention may be advantageously employed as a single, unit, or as .a component part of more elaborate purification systemt, Y

I claim: "-1. The method of purifying and drying sulfur dioxide burner gas containing fluorine impurities V 'which comprisescontacting the gas with sulfuric a'cidof over 98% strength, whereby the gas is dried and fluorine impurities removed therefrom. 15

" Z. In the method'of cooling and purifying hot fluorine containing burner gas in the contact sulfuriciacid process involving contacting the gas with sulfuric acid whereby the gas is cooled, solid impurities removed therefromand the moisture 20 7 content thereof increased, further cooling the'. gas

and separating moisture ,andsulfurio' acicltinist therefrom, the improvement ilwhich comprisesfi' then contacting thegas, with sulfuric acid ofuoyer:

98% strength, whereby thefigasisudriediand-fiuoe.25; V I rine impurities removed therefromr; 3. The improvementgin the;contact'process for/ V the manufacture of sulfuric acid in which sulfu dioxide gas containing fluorine impurities 'is'sub, jected to purificationaand then contacted with, i, platinum catalyst, which comprises subjecting the gas as a part of the .purificationtreatrnent tocon-u.

, tact with sulfuricacid-ofoyerro98%,strength and then passing the gasin' contact-with the catalysav:

4. The method of purifying and drying-,sulfur-T' g dioxide burner gas containing hydrofluoric,acidinw excess of. 0.0000001 gram ;per,cubic: fo ot.which" comprises contacting the gas :with sulfuric: acid" of over 98% strength, whereby the gas is driedia and fluorine removed therefrom.

r '40 JESSE G.1MELENDY. ,z; 

